Intimidating Presence allows you to use intimidation options in conversation, which can reduce the leg-work in some quests. It also allows you to rob from some merchants you may find on the road, which can earn you the Crime Pays achievement. Intimidation options are easily recognized, as they begin with the text: "[Intimidate]", and are usually in red text. Since Update 12(?), it also reduces the Stamina cost of all Fighters Guild abilities.